AU4744599A

AU4744599A - Method and apparatus for idle handoff in a cellular system

Info

Publication number: AU4744599A
Application number: AU47445/99A
Authority: AU
Inventors: Sang-Tae Kim; Young-Sik Lim
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1998-09-08
Filing date: 1999-09-08
Publication date: 2000-03-16
Anticipated expiration: 2019-09-08
Also published as: CN1248138A; US6400952B2; JP3126706B2; JP2000092552A; KR100291478B1; AU731563B2; CN1110217C; KR20000019061A; US20010016493A1

Description

P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT 4* Name of Applicant: Actual Inventor Samsung Electronics Co, Ltd Sang-Tae Kim and Young-sik Lim WRAY ASSOCIATES 239 Adelaide Terrace Perth, WA 6000 Address for service is: Attorney code: WR Invention Title: Method And Apparatus For Idle Handoff In A Cellular System The following statement is a full description of this invention, including the best method of performing it known to me:- -2-

TITLE

Method And Apparatus For Idle Handoff In A Cellular System FIELD OF THE INVENTION The current invention relates to a method and apparatus for executing an idle handoff in a cellular system. More specifically, a method and apparatus for executing a handoff in a conventional code division multiple access (CDMA) system when a mobile terminal in an idle state, moves between base stations having different frequency assignments

(FA).

DESCRIPTION OF RELATED ART In a cellular communications system having a plurality of cells which are divided into sub-sets, and where each of these sub-sets is controlled by a base station, it .is possible to maintain communication with a MT by using a handoff function when the MT moves between cells.

A handoff is a function for the cellular system to maintain communication with a MT that is in communication with a first base station (BS) as the MT moves into another BS's coverage region.

Conventional cellular systems comprise MT for providing communication services to users, BSs for providing service to MTs, and base station controllers (BSCs) for controlling the BSs, along with mobile switching centre (MSC) for providing communications between the BSCs and a public switch telephone network (PSTN).

When an MT is powered up and is not engaged on a call it is in an idle state where it monitors the paging channel the base station it is currently synchronised with.

-3- The MT uses the paging channel of BSs to receive messages from BSs, to receive information on inbound calls, and to initialise outgoing calls. In the idle state, an MT also monitors paging channels of surrounding BSs. When the MT moves from a coverage area of a first BS to the coverage area of a neighbouring BS the MT performs an idle handoff from the first BS to the second BS.

In CDMA systems, channels transmitted from a BS have a pseudo-random noise (PN) sequence offset value which is called a pilot signal. Each base station is identified by its PN sequence in its pilot signal. MTs operate to identify base stations by use of their pilot signals.

10 When an MT detects a pilot signal of a neighbouring BS of greater strength than the strength of the pilot signal of the MTs current base station, the MT executes an idle handoff to the new cell. The MT and the BS of the second cell then recognise the MT as being handed off.

In a CDMA system, neighbouring BSs may have different frequency assignments (FAs). Accordingly when an MT moves from one BS with a first FA into a neighbouring BS with a second FA, the MT detects a dummy pilot signal transmitted by the second BS at the first FA.

ooo° Each BS is required to broadcast dummy pilot signals at each one of the FAs of their neighbouring BSs as MTs only have provision for operating at a single FA at any one point in time.

Detection of a pilot signal dummy or otherwise at sufficient signal strength enables the MT to determine that it has entered into the coverage area of another BS. To execute an idle handoff to the new BS, the MT firstly initiates a handoff from the previous BS to the new BS. The MT, once handed off to the new BS is instructed to perform a frequency handoff to the FA of the new BS.

This enables the MT to monitor to the paging channel of the new BS.

This prior art handoff method has some complexities owing to the execution of a two stage idle handoff process that includes an inter-cell handoff to the new BS -4followed by an inter-frequency handoff once in the new BS. If an inbound call from a user occurs before the inter-cell handoff and inter-frequency handoff are finished, the call cannot be terminated with the MT.

DISCLOSURE OF THE INVENTION According to a first aspect of the present invention there is provided a mobile terminal for use in a cellular communications network having a plurality of base stations and at least two frequency assignments for said base stations; the mobile terminal adapted to assume an idle state when available to receive an inbound call from said network; to synchronise with a first base station when in 10 said idle state and to receive neighbour information from said first base station comprising at least data on frequency assignments of neighbouring base stations of said first base station; the mobile terminal further adapted to monitor pilot signals and dummy pilot signals of said first base station and said neighbouring S: base stations whereby said mobile terminal is adapted to select a second base 15 station for executing an idle handoff with under predetermined conditions and wherein said mobile terminal identifies the frequency assignment of said second base station prior to effecting said idle handoff and selects an idle handoff procedure dependent on said frequency assignment of said second base station.

Preferably, said mobile terminal identifies the frequency assignment of said second base station in response to detecting a dummy pilot signal of said second base station.

Preferably, said mobile terminal identifies a pilot signal as a dummy pilot signal from said neighbour information.

Preferably, said mobile terminal is adapted to monitor a paging channel of said second base station in response to identify that said second base station has a frequency assignment corresponding to said first base station Preferably, said mobile terminal in response to detecting a dummy pilot signal of said second base station effects a frequency handoff to said frequency assignment of said second base station prior to effecting said idle handoff to said second base station.

Preferably, said mobile terminal monitors a paging channel of said second base station subsequent to said frequency handoff and prior to said idle handoff.

Preferably, said mobile terminal in response to detecting a dummy pilot signal of said second base station effects an idle handoff to said second base station at the frequency assignment of the second base station.

Preferably, said neighbour information comprises at least one of the following data sets for each of said neighbouring base station of said first base station: *10 1) an index of the pilot pseudo-random noise offset (PILOTPN); 2) configuration state of the frequency assignment (NGHBR_CONFIG); 3) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); 4) frequency band information indicating the frequency band of signals 15 (NGHBR_BAND); and assigned frequency information indicating the frequency assignment

(NGHBR_FREQ).

According to a second aspect of the present invention there is provided a method of operating a cellular communications network comprising at least a first base station having a first frequency assignment and at least a second base station having a second frequency assignment; the method comprising the steps of: 1) said first and second base stations performing an idle handoff of a mobile terminal from said first base station to said second base station; -6- 2) said second base station transmitting frequency assignment information to said mobile terminal; said frequency assignment information identifying frequency assignments of base stations neighbouring said second base station.

Preferably said method further comprises, the step 30 of said second base station receiving an idle hand off request from said mobile terminal; and 4) said second base station performing said requested hand off.

Preferably, step 3) further comprises said second base station receiving said hand off request from said mobile terminal in response to said mobile terminal 10 receiving said frequency assignment information and using said frequency assignment information to determine the frequency assignment of said neighbouring base station whereby said mobile terminal selects an handoff procedure dependent on said frequency assignment.

Preferably, said first and second base stations each transmit a pilot signal and a 15 dummy pilot signal and wherein step 2) further comprises transmission of at least 00.o one of the following data sets: 1) an index of the pilot pseudo-random noise offset (PILOT_PN); 2) configuration state of the frequency assignment

(NGHBR_CONFIG);

3) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); 4) frequency band information indicating the frequency band of signals (NGHBR_BAND); and assigned frequency information indicating the frequency assignment

(NGHBR_FREQ).

-7- According to a third aspect of the present invention there is provided a method for performing an idle hand off between base stations of a cellular communications system having multiple frequency assignments for base stations; said method comprising the steps of: 1) a mobile terminal synchronised with a first base station detecting a pilot signal of a second base station; 2) identifying whether or not said pilot signal is a dummy pilot signal; determining the frequency assignment of said second base station in response to identifying said pilot signal as a dummy pilot signal; 10 and 4) performing said idle hand off to said second base station at said frequency assignment.

Preferably, step 1) further comprises said first base station transmitting to said mobile terminal neighbour information comprising at least information on the 15 frequency assignments of neighbouring base stations of said first base station; and steps 2) 3) executed by said mobile terminal by referencing said neighbour information.

Preferably, step 4) further comprises said mobile terminal monitoring a paging channel of said second base station prior to effecting said idle hand off.

Preferably, step 4) further comprises said mobile terminal performing a frequency hand off to the frequency assignment of said second base station in response to identifying at step 2) that said pilot signal is a dummy pilot; and said mobile terminal monitoring said paging channel subsequent to said frequency hand off and prior to said idle hand off.

Preferably, said mobile terminal performs a frequency hand off to the frequency assignment of said second base station in response to identifying (at step 2) that -8said pilot signal is a dummy signal; and said mobile terminal performing said frequency hand off in conjunction with said idle hand off.

Preferably, said mobile terminal monitors a paging channel of said second base station in response to identifying at step 2) that said pilot signal is not a dummy pilot signal.

Preferably, said neighbour information of step 1) further comprises a list of neighbouring base stations and wherein step 2) further comprises identifying whether or not said second base station is in said list and determining that said idle hand off procedure has failed if said second base station is absent from said 10 list.

oo°° Preferably, said mobile terminal effects said idle handoff subsequent to identifying that said second base station exceeds in strength the pilot signal of said first base station by a pre determined amount.

Preferably, said neighbour information includes at least one of the following data 15 sets for each said neighbouring base station: 1) an index of the pilot pseudo-random noise offset (PILOT_PN); 2) configuration state of the frequency assignment (NGHBR_CONFIG); 3) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); 4) frequency band information indicating the frequency band of signals (NGHBR_BAND); and assigned frequency information indicating the frequency assignment

(NGHBR_FREQ).

According to a fourth aspect of the present invention there is provided a method of operating a mobile terminal for use in a cellular communications network having a plurality of base stations and at least two frequency assignments for said base stations; the method comprising the steps of said mobile terminal assuming an idle state when available to receive an inbound call from said network; synchronising with a first base station when in said idle state and receiving neighbour information from said first base station comprising at least data on frequency assignments of neighbouring base stations of said first base station; monitoring pilot signals and dummy pilot signals of said first base station and said neighbouring base stations and whereby selecting a second base station for executing an idle handoff with under predetermined conditions; identifying the frequency assignment of said second base station prior to effecting said idle handoff; and selecting an idle handoff procedure dependent on said frequency assignment of said second base station.

Preferably said method of operating a mobile terminal further comprises the step aof identifying the frequency assignment of said second base station in response to detecting a dummy pilot signal of said second base station.

Preferably said method of operating a mobile terminal further comprises the step of identifying a pilot signal as a dummy pilot signal from said neighbour information.

Preferably said method of operating a mobile terminal further comprises the step of monitoring a paging channel of said second base station in response to identify that said second base station has a frequency assignment corresponding to said first base station.

Preferably said method of operating a mobile terminal further comprises the step of effecting a frequency handoff to said frequency assignment of said second base station prior to effecting said idle handoff to said second base station in response to detecting a dummy pilot signal of said second base station.

Preferably said method of operating a mobile terminal further comprises the step of monitoring a paging channel of said second base station subsequent to said frequency handoff and prior to said idle handoff.

Preferably said method of operating a mobile terminal further comprises the step of detecting a dummy pilot signal of said second base station effects an idle handoff to said second base station at the frequency assignment of the second base station.

Preferably said method of operating a mobile terminal further comprises said neighbour information having at least one of the following data sets for each of 10 said neighbouring base station of said first base station: ooo 6) an index of the pilot pseudo-random noise offset (PILOT PN); 7) configuration state of the frequency assignment (NGHBR_CONFIG); 8) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); 00..

0 9) frequency band information indicating the frequency band of signals 0 00 00.(NGHBR_BAND); and assigned frequency information indicating the frequency assignment

(NGHBR_FREQ).

According to a fifth aspect of the present invention there is provided a cellular communications network comprising at least a first base station having a first frequency assignment and at least a second base station having a second frequency assignment; the network operated according to the steps of: 3) said first and second base stations performing an idle handoff of a mobile terminal from said first base station to said second base station; -11- 4) said second base station transmitting frequency assignment information to said mobile terminal; said frequency assignment information identifying frequency assignments of base stations neighbouring said second base station.

Preferably said cellular communications network is operated according to the further step 3) of said second base station receiving an idle hand off request from said mobile terminal; and 4) said second base station performing said requested hand off.

Preferably said cellular communications network is operated according to step 3) further comprising said second base station receiving said hand off request from oo°said mobile terminal in response to said mobile terminal receiving said frequency assignment information and using said frequency assignment information to determine the frequency assignment of said neighbouring base station whereby said mobile terminal selects an handoff procedure dependent on said frequency assignment.

",.Preferably said cellular communications network is operated according to said first and second base stations each transmitting a pilot signal and a dummy pilot signal and wherein step 2) further comprises transmission of at least one of the following data sets: 1) an index of the pilot pseudo-random noise offset (PILOT_PN); 2) configuration state of the frequency assignment (NGHBR_CONFIG); 3) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); 4) frequency band information indicating the frequency band of signals (NGHBR_BAND); and -12assigned frequency information indicating the frequency assignment

(NGHBR_FREQ).

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention shall now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 illustrates a conventional cellular system using the CDMA technology; Figure 2 is a flow chart for illustrating a first preferred embodiment of an idle handoff method; Figure 3 is a flow chart for illustrating a second preferred embodiment of an idle 10 handoff method; and Figure 4 is a flow chart for illustrating a third preferred embodiment of an idle handoff method in a cellular system.

BEST MODE(S) FOR CARRYING OUT THE INVENTION **Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

In a CDMA cellular communication system, an MT is said to be in an "idle" state when the MT is active, in the sense that it is monitoring the network for incoming calls but is not actually engaged on a call. When an MT is in an "idle" state it is synchronised with the BS whose coverage area it is presently located within and it monitors the paging channels of this BS. The paging channels are used by the BS to notify the MT of inbound calls and other messages.

-13- As the MT moves from cell to cell it is necessary for the MT to re-register with the BS in each cell where it is presently located. This is so that the cellular network knows which BS to route inbound calls to in order to terminate the call with the correct MT. Hence an MT moving from cell to cell must continuously re-register with each BS of each cell that it enters, in order for the MT to maintain an operational connection with the network.

Additional complexities arise where neighbouring BSs have differing FAs. These complexities arise because most MTs only have capacity to listen to one frequency at any one time. Hence, as an MT moves from a first BS with a first 10 FA to a second BS with a second FA, the MT is unable to detect the pilot signal of the second BS. Hence, the MT is unable to detect that it has entered the service area of the second BS.

o°°ooo, S S. To overcome this problem, BSs transmit dummy pilot signals that are at the FA of its neighbouring BSs. Hence a MT that is registered with a first BS at a first 15 FA is able to detect the dummy pilot signal of a second BS, so long as the dummy pilot signal is transmitted at the FA of the BS that the MT is currently S°registered with.

The present embodiments utilise the dummy pilot signal of a neighbouring BS to determine, not only that MTs need to perform an idle handoff to a new BS, but also to determine that the MTs need to perform a frequency handoff in order to listen the paging channels of the new BS. By providing MTs with advance knowledge of the FA of neighbouring base stations, the MTs are able to execute a frequency handoff, either simultaneously with, or prior to, execution of an intercell handoff from the MTs current base station to the new base station whose coverage area the MT has moved into.

This provides an advantage in that idle handoff of an MT from one BS to another BS can be performed with greater speed and less network overhead. This increases quality of service to the users of the cellular network and also increases network capacity.

-14- Referring now to Figure 1 which is an illustration of a cellular communication system. The network comprises a first BS 30 and a second BS 31 that are controlled by a BSC 20. The BSC 20 is in communication with an MSC 10 and the MSC 10 is in communication with a PSTN 11. The MSC 10 has a home location register (HLR) and a visitor location register (VLR) 13.

The HLR stores a record of the MTs that normally reside within control of the MSC 10. The HLR 12 also stores a record of the last BS that each mobile in the HLR 12 was registered with.

The VLR 13 stores a record of the MTs that are normally controlled by another 10 MSC and that are presently under the control of the MSC first BS 30 operates over a first cell 1. The second BS 31 operates over a second cell 2. The first cell 1 and the second cell 2 have an overlapping area where each of the first BS 30 and the second BS 31 is able to provide service to a MT. This area is commonly referred to as a soft handoff region.

15 A user 40 is depicted as being located within this area of overlap between the ",.first cell 1 and the second cell 2. An arrow indicates that the user 40 is moving from the first cell 1 into the second cell 2. Accordingly, the user 40 is about to perform an idle handoff from the first BS 30 to the second BS 31.

The first BS 30 has a first frequency assignment FA 1 and the second BS 31 has a second frequency assignment FA 2. Accordingly as part of the idle handoff, the MT operated by the user 40 needs to perform an inter-cell handoff and an inter-frequency handoff.

When the user 40 entered the first cell 1 the MT (operated by the user received information from the first BS 30. This information is referred to as the neighbour list message.

It is preferable that the neighbour list message includes: an index of pilot pseudorandom noise offset (PILOTPN); a configuration state of the frequency assignment of the neighbouring base station (NGHBR_CONFIG); frequency indicator information to indicate which pilot signals of the neighbouring BSs the MT will detect as being dummy pilot signals, due to the FA of the MTs current BS (FREQ_INCL); frequency band information that indicates the band of frequencies assigned to neighbouring BSs (NGHBR_BAND); and assigned frequency information that indicates the FAs of neighbouring BSs (NGHBR_FREQ).

The MT controlled by the user 40 receives this extended neighbour list information upon registering with the first BS 30, if the MT is powered up by the user 40 whilst in the first cell 1 or if the MT executes an idle handoff to the first 10 cell 1 from another cell not shown in the present diagram.

The extended neighbour list information enables the MT to determine in advance 'o of executing an idle handoff what the FA is, of the BS that the MT is being handed off to.

Referring now to Figure 2 which is a procedure for effecting an idle handoff. The procedure commences at step s10 where the user 40 enters the first cell 1 and receives information transmitted by the first BS 30 relating to FAs of the second BS 31 and any other BSs that neighbour the first BS 30 (and that are not represented in Figure 1).

This information on the FAs of the neighbouring BS contains information such as that of Table 1.

FIELDS LENGTH (BITS) EXAMPLE PILOTPN 9 472 NGHBR_CONFIG 3 2 FREQ INCL 1 1 -16- NGHBR BAND 0 OR5 1 NGHBRFREQ 0 OR 11 300 TABLE 1 The information on neighbouring BSs, such as the extended neighbour list, is stored in the mobile terminal operated by the user At step s20, the user 40 moves from the first cell 1 into a region where it detects the pilot signal of the second BS 31.

After detecting the pilot signal of the second BS 31, the mobile terminal operated r°a..by the user 40 determines whether or not the pilot signal that has been detected is from a BS included in the list of neighbouring BSs that was transmitted by the first BS 30 at step sl0.

S 10 If the answer to step s30 is negative then the process proceeds to step s40 and the idle handoff is regarded as having failed.

If at step s30, the pilot signal is from a BS that is in the list of neighbouring BSs then the process moves to step s50 where the MT operated by the user determines whether or not the detected pilot signal is a dummy pilot signal.

If at step s50 the pilot signal that is detected is not a dummy pilot signal then the process moves to step s80 where the MT operated by user 40 detects a paging channel of the second BS 31. The MT of the user 40 is able to detect this paging channel by utilising the information transmitted to it at step s10. After step the network is able to effect a handoff of the MT from the first BS 30 to the second BS 31 during which the MT listens to the paging channel of the second BS 31.

Messages received on the paging channel of the first BS 30 and not processed by the MT may be discarded.

-17- If at step s50 a dummy pilot signal is detected then the process proceeds to step where the MT operated by user 40 reviews the information transmitted to it by the first BS at step s10 to identify the FA of the second BS 31.

Having determined the appropriate frequency of the second BS 31, the MT at step s70 executes a frequency handoff and commences listening to the paging channel of the second BS 31, after which the network effects an inter-cell handoff of the MT from the first BS 30 to the second BS 31.

Referring now to Figure 3 which is an alternate embodiment for executing an idle handoff. The process commences with steps s100 through steps s130 which are 10 similar to steps s10 through s50 of Figure 2.

Step s130 is the detection of a pilot signal by the MT operated by user 40. In this embodiment, if step s130 is negative, and the detected pilot signal is not a dummy pilot signal, then the process moves to step s150 where an idle handoff according to known methods is executed.

g* 15 If however, at step s130 the detected pilot signal is a dummy pilot signal then the process moves to step s140 where the MT interrogates the information transmitted by the first BS 30 at step s100 (this information being information similar to that transmitted by the first BS 30 at step s10 of Figure From this interrogation the MT determines the FA of the second BS 31 that the MT is to be handed off to.

The process then moves to step s150 where an idle handoff is executed at the FA of the second BS 31 as determined at step s140.

By determining the handoff frequency in advance of executing the handoff, the additional step of an inter-frequency handoff once the MT has been handed off to the second BS 31 is eliminated. This reduces the time taken to perform an idle handoff. It also reduces network overheads.

-18- Referring now to Figure 4 which is a further embodiment for effecting an idle handoff. This embodiment is particularly related to the process that is executed within the MT operated by user The process commences with the MT synchronised with the first BS 30. At step s210 the MT detects a pilot signal transmitted by the second BS 31.

At step s220 the MT determines whether or not the pilot signal that has been S- detected is included in the extended neighbours list that was previously transmitted to the MT by the first BS 30. This extended neighbour list information typically the information transmitted at step sl0 of Figure 2.

If the outcome of step s220 is that the detected pilot signal is not a pilot signal transmitted from a neighbouring base station then at step s230 the MT *determines that the idle handoff procedure has failed. The MT then executes procedures according to standard protocols, such as interface protocol IS-95 to *OOS* re-initialise itself with the network.

S

If at step s220 the MT determines that the detected pilot signal is from a neighbouring BS of the first BS 30, then the MT proceeds to step s240 where it determines whether or not the pilot signal is a dummy pilot signal.

If at step s240 the detected pilot signal is not a dummy pilot signal, then the MT proceeds to step s250 where it executes an inter-cell idle handoff according to known procedures. This inter-cell idle cell handoff is efficient in operation as the MT is not required to execute an inter-frequency handoff once it has been handed off to the second BS 31. Hence the MT has utilised the information inherent in the pilot signal in that detection of a dummy pilot signal indicates that an inter-frequency handoff will be required of the MT when handed off.

If at step s240 the MT determines that the pilot signal is a dummy pilot signal then the MT proceeds to step s260 where it interrogates the extended neighbour list that was previously transmitted to the MT from the first BS 30. This -19interrogation of the extended neighbour list allows the MT to determine the FA that it will need to utilise once handed off to the second BS 31.

Having determined the FA that the MT will require once handed off to the second BS 31, the MT proceeds to step s270 where it executes an inter-cell handoff to the second BS 31 at the FA of the second BS 31.

Again the additional step of executing an inter-frequency handoff once the MT executed an inter-cell handoff to the second BS 31 is eliminated. This additional step is eliminated through utilising the information inherent in the detected pilot signal namely that a dummy pilot signal indicates that an inter- 10 frequency handoff will be required in addition to the inter-cell handoff.

Utilisation of this additional information inherent in the pilot signal, or dummy pilot *signal is facilitated by the additional information transmitted to the MT by its current BS, such as the information transmitted at step sl0 of Figure 2 or step sl00 of Figure 3.

15 It is preferable that in detecting pilot signals and dummy pilot signals that the MT execute idle handoffs according to procedures well known in the art, such as only executing an idle handoff once the detected pilot signal has a strength that exceeds the strength of the pilot signal of the BS that the MT is currently synchronised with. It is preferable that this strength is of a predetermined value such as 3dB.

It is not essential that the information transmitted by the current BS of the MT, such as the information transmitted at step slO of Figure 2 and step sl00 of Figure 3 includes the extended neighbour information detailed herein. However, it is preferred that at least some information on the FA of neighbouring BSs of the first BS 30 is transmitted during these steps. Knowledge of these FAs enables the MT to utilise the information inherent in the detected pilot signals as to whether or not the MT will be required to execute an inter-frequency handoff once it has executed an inter-cell handoff.

Claims

1. A mobile terminal for use in a cellular communications network having a plurality of base stations and at least two frequency assignments for said base stations; the mobile terminal adapted to assume an idle state when available to receive an inbound call from said network; to synchronise with a first base station when in said idle state and to receive neighbour information from said first base station comprising at least data on frequency assignments of neighbouring base stations of said first base station; the mobile terminal further adapted to monitor pilot signals and dummy pilot o 10 signals of said first base station and said neighbouring base stations whereby said mobile terminal is adapted to select a second base station for executing an idle handoff with under predetermined conditions and wherein said mobile terminal identifies the frequency assignment of said second base station prior to effecting said idle handoff and selects an idle handoff procedure 15 dependent on said frequency assignment of said second base station.

2. A mobile terminal as claimed in claim 1, wherein said mobile terminal identifies the frequency assignment of said second base station in response to detecting a dummy pilot signal of said second base station.

3. A mobile terminal as claimed in anyone of claim 1 or claim 2 wherein said mobile terminal identifies a pilot signal as a dummy pilot signal from said neighbour information.

4. A mobile terminal as claimed in any one of claims 1 to 3 wherein said mobile terminal is adapted to monitor a paging channel of said second base station in response to identify that said second base station has a frequency assignment corresponding to said first base station A mobile terminal as claimed in any one of claims 2 to 4, wherein said mobile terminal in response to detecting a dummy pilot signal of said second base station effects a frequency handoff to said frequency assignment of said -21 second base station prior to effecting said idle handoff to said second base station.

6. A mobile terminal as claimed in claim 5, wherein said mobile terminal monitors a paging channel of said second base station subsequent to said frequency handoff and prior to said idle handoff.

7. A mobile terminal as claimed in any one of claims 1 to 4, wherein said mobile o terminal in response to detecting a dummy pilot signal of said second base station effects an idle handoff to said second base station at the frequency assignment of the second base station.

8. A mobile terminal as claimed in any one of the preceding claims, wherein said neighbour information comprises at least one of the following data sets for each of said neighbouring base station of said first base station: an index of the pilot pseudo-random noise offset (PILOTPN); 7) configuration state of the frequency assignment (NGHBR_CONFIG); 8) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); 9) frequency band information indicating the frequency band of signals (NGHBR_BAND); and assigned frequency information indicating the frequency assignment (NGHBR_FREQ).

9. A method of operating a cellular communications network comprising at least a first base station having a first frequency assignment and at least a second base station having a second frequency assignment; the method comprising the steps of:

22- 3) said first and second base stations performing an idle handoff of a mobile terminal from said first base station to said second base station; 4) said second base station transmitting frequency assignment information to said mobile terminal; said frequency assignment information identifying frequency assignments of base stations neighbouring said second base station. A method of operating cellular communications system as claimed in claim 9 :...further comprising the step 3) of said second base station receiving an idle 10 hand off request from said mobile terminal; and 4) said second base station performing said requested hand off. 11. A method of operating a cellular communications system as claimed in claim *10 wherein step 3) further comprises said second base station receiving said hand off request from said mobile terminal in response to said mobile 15 terminal receiving said frequency assignment information and using said frequency assignment information to determine the frequency assignment of said neighbouring base station whereby said mobile terminal selects an handoff procedure dependent on said frequency assignment. 12. A method of operating a cellular communications network as claimed in any one of claims 9 to 11, wherein said first and second base stations each transmit a pilot signal and a dummy pilot signal and wherein step 2) further comprises transmission of at least one of the following data sets: 1) an index of the pilot pseudo-random noise offset (PILOT_PN); 2) configuration state of the frequency assignment (NGHBR_CONFIG); 3) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); -23- 4) frequency band information indicating the frequency band of signals (NGHBR_BAND); and assigned frequency information indicating the frequency assignment (NGHBR_FREQ). 13. A method for performing an idle hand off between base stations of a cellular communications system having multiple frequency assignments for base stations; said method comprising the steps of: 1) a mobile terminal synchronised with a first base station detecting a S:o, pilot signal of a second base station; 10 2) identifying whether or not said pilot signal is a dummy pilot signal; 3) determining the frequency assignment of said second base station in response to identifying said pilot signal as a dummy pilot signal; and 4) performing said idle hand off to said second base station at said frequency assignment. 14. A method as claimed in claim 13 wherein step 1) further comprises said first base station transmitting to said mobile terminal neighbour information comprising at least information on the frequency assignments of neighbouring base stations of said first base station; and steps 2) 3) executed by said mobile terminal by referencing said neighbour information. A method as claimed in any one of claims 13 or 14 wherein step 4) further comprises said mobile terminal monitoring a paging channel of said second base station prior to effecting said idle hand off. 16. A method as claim in claim 15 wherein step 4) further comprises said mobile terminal performing a frequency hand off to the frequency assignment of said -24- second base station in response to identifying at step 2) that said pilot signal is a dummy pilot; and said mobile terminal monitoring said paging channel subsequent to said frequency hand off and prior to said idle hand off. 17. A method as claimed in any one of claims 13 or 14 wherein said mobile terminal performs a frequency hand off to the frequency assignment of said second base station in response to identifying at step 2) that said pilot signal is a dummy signal. 99 18. A method as claimed in any one of claims 13 to 16 wherein said mobile terminal monitors a paging channel of said second base station in response ooO 10 to identifying at step 2) that said pilot signal is not a dummy pilot signal. 19. A method as claimed in any one of claims 13 to 18 wherein said neighbour information of step 1) further comprises a list of neighbouring base stations and wherein step 2) further comprises identifying whether or not said second base station is in said list and determining that said idle hand off procedure has failed if said second base station is absent from said list. A method as claimed in any one of claims 13 to 19 wherein said mobile terminal effects said idle handoff subsequent to identifying that said second base station exceeds in strength the pilot signal of said first base station by a pre determined amount. 21. A method as claimed in any one of claims 13 to 20 wherein said neighbour information includes at least one of the following data sets for each said neighbouring base station: 6) an index of the pilot pseudo-random noise offset (PILOT_PN); 7) configuration state of the frequency assignment (NGHBR_CONFIG); 8) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); L 9) frequency band information indicating the frequency band of signals (NGHBR_BAND); and frequency information indicating the frequency assignment (NGHBR_FREQ). 22. A method of operating a mobile terminal for use in a cellular communications network having a plurality of base stations and at least two frequency assignments for said base stations; the method comprising the steps of said eo mobile terminal assuming an idle state when available to receive an inbound call from said network; synchronising with a first base station when in said 10 idle state and receiving neighbour information from said first base station comprising at least data on frequency assignments of neighbouring base stations of said first base station; monitoring pilot signals and dummy pilot signals of said first base station and said neighbouring base stations and whereby selecting a second base station for executing an idle handoff with 15 under predetermined conditions; identifying the frequency assignment of said second base station prior to effecting said idle handoff; and selecting an idle **handoff procedure dependent on said frequency assignment of said second base station.

23. A method as claimed in claim 22, further comprising the step of identifying the frequency assignment of said second base station in response to detecting a dummy pilot signal of said second base station.

24. A method as claimed in anyone of claims 22 or claim 23 further comprising the step of identifying a pilot signal as a dummy pilot signal from said neighbour information.

25. A method as claimed in any one of claims 22 to 24 further comprising the step of monitoring a paging channel of said second base station in response to identify that said second base station has a frequency assignment corresponding to said first base station. I P 26

26. A method as claimed in any one of claims 23 to 25, further comprising the step of effecting a frequency handoff to said frequency assignment of said second base station prior to effecting said idle handoff to said second base station in response to detecting a dummy pilot signal of said second base station.

27. A method as claimed in claim 26, further comprising the step of monitoring a paging channel of said second base station subsequent to said frequency handoff and prior to said idle handoff.

28. A method as claimed in any one of claims 22 to 25, further comprising the 10 step of detecting a dummy pilot signal of said second base station effects an idle handoff to said second base station at the frequency assignment of the second base station.

29. A method as claimed in any one of claims 22 to 28, wherein said neighbour information comprises at least one of the following data sets for each of said neighbouring base station of said first base station: 11) an index of the pilot pseudo-random noise offset (PILOTPN); 12) configuration state of the frequency assignment (NGHBR_CONFIG); 13) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); 14) frequency band information indicating the frequency band of signals (NGHBR_BAND); and assigned frequency information indicating the frequency assignment (NGHBR_FREQ). A cellular communications network comprising at least a first base station having a first frequency assignment and at least a second base station 4 1 t 27 having a second frequency assignment; the network operated according to the steps of: said first and second base stations performing an idle handoff of a mobile terminal from said first base station to said second base station; 6) said second base station transmitting frequency assignment *information to said mobile terminal; said frequency assignment information identifying frequency assignments of base stations neighbouring said second base station.

31. A cellular communications system as claimed in claim 30 operated according to the further step 3) of said second base station receiving an idle hand off request from said mobile terminal; and 4) said second base station performing said requested hand off.

32. A cellular communications system as claimed in claim 31 wherein step 3) further comprises said second base station receiving said hand off request from said mobile terminal in response to said mobile terminal receiving said frequency assignment information and using said frequency assignment information to determine the frequency assignment of said neighbouring base station whereby said mobile terminal selects an handoff procedure dependent on said frequency assignment.

33. A cellular communications network as claimed in any one of claims 30 to 32, wherein said first and second base stations each transmit a pilot signal and a dummy pilot signal and wherein step 2) further comprises transmission of at least one of the following data sets: 6) an index of the pilot pseudo-random noise offset (PILOT_PN); 7) configuration state of the frequency assignment (NGHBR_CONFIG); 1 j. i. -28- 8) frequency indicator information to indicate whether or not the pilot signal is a dummy pilot signal (FREQ_INCL); 9) frequency band information indicating the frequency band of signals (NGHBR_BAND); and 10) assigned frequency information indicating the frequency assignment (NGHBR FREQ). Dated this Eighth day of September 1999. Samsung Electronics Co, Ltd S" Applicant Wray Associates Perth, Western Australia Patent Attorneys for the Applicant